fix(worker): add standalone entry point for K8s deployment

- 新增 __main__ 入口點
- 寫入 health files for K8s probes
- Graceful shutdown 處理

Co-Authored-By: Claude <noreply@anthropic.com>

apps/api/src/workers/signal_worker.py

@@ -292,3 +292,78 @@ def get_signal_worker() -> SignalWorker:
             "Signal worker not initialized. Call init_signal_worker() first."
         )
     return _signal_worker
+
+
+# =============================================================================
+# Standalone Entry Point (for K8s Worker Deployment)
+# =============================================================================
+
+async def _write_health_files() -> None:
+    """
+    Write health check files for K8s probes.
+    """
+    from pathlib import Path
+
+    Path("/tmp/worker-healthy").touch()
+    Path("/tmp/worker-ready").touch()
+    logger.info("health_files_written")
+
+
+async def _main() -> None:
+    """
+    Standalone worker main function.
+
+    用於 K8s Deployment 直接執行:
+    python -m src.workers.signal_worker
+    """
+    import signal
+    import sys
+
+    # Initialize settings first (loads env vars)
+    from src.core.config import settings  # noqa: F401
+    from src.core.redis_client import init_redis, close_redis
+
+    logger.info(
+        "signal_worker_standalone_starting",
+        environment=settings.ENVIRONMENT,
+        redis_url=settings.REDIS_URL.split("@")[-1] if settings.REDIS_URL else "N/A",
+    )
+
+    # Initialize Redis
+    await init_redis()
+
+    # Write health files for K8s probes
+    await _write_health_files()
+
+    # Initialize and start worker
+    worker = await init_signal_worker()
+
+    # Setup graceful shutdown
+    shutdown_event = asyncio.Event()
+
+    def _shutdown_handler(signum: int, frame: object) -> None:
+        logger.info("shutdown_signal_received", signal=signum)
+        shutdown_event.set()
+
+    signal.signal(signal.SIGTERM, _shutdown_handler)
+    signal.signal(signal.SIGINT, _shutdown_handler)
+
+    # Wait for shutdown signal
+    await shutdown_event.wait()
+
+    # Graceful shutdown
+    logger.info("signal_worker_shutting_down")
+    await worker.stop()
+    await close_redis()
+
+    # Remove health files
+    from pathlib import Path
+    Path("/tmp/worker-healthy").unlink(missing_ok=True)
+    Path("/tmp/worker-ready").unlink(missing_ok=True)
+
+    logger.info("signal_worker_shutdown_complete")
+    sys.exit(0)
+
+
+if __name__ == "__main__":
+    asyncio.run(_main())